Metal salt flocculant

Abstract

To provide a metal salt flocculant containing iron ion and aluminum ion that has higher storage stability and flocculation capacity by mixing and combining poly ferric sulfate and polyaluminum chloride compared to the case that each is used alone, and further, can be applied for a wide range of treated effluents with various characteristics, and further, to provide a metal salt flocculant which has also coli bacillus removal action.SOLUTION: In 1 liter of a metal salt flocculant, the sum of contents of aluminum ion and iron ion is 5.7 mol or less, a molar ratio (Cl / Fe) of iron ion to chlorine ion is 28 or more, a molar ratio (SO4 / Al2O3) of aluminum ion in terms of aluminum oxide to sulfate ion is 0.15 or less. The metal salt flocculant has a coli bacillus removal ratio of 83% or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a metal salt flocculant containing iron ions and aluminum ions and various chemicals used in wastewater treatment. The present invention also relates to a metal salt flocculant and various chemicals having an Escherichia coli removing effect.

Background Art

[0002] In sewage treatment plants and night soil treatment plants, iron-based or aluminum-based metal salt flocculants are added to treated water and the like for the purpose of improving the quality of the discharged water, reducing the amount of waste, smooth operation of the facilities, and extending the service life. Representative iron-based flocculants include ferric chloride, poly ferric sulfate, and ferrous sulfate solution, and aluminum-based ones include band sulfate, aluminum chloride, and polyaluminum chloride.

[0003] Poly ferric sulfate is one of the representative examples of iron-based inorganic flocculants and has a deodorizing and dephosphorizing effect, so it is widely used in sewage treatment plants and night soil treatment. Poly ferric sulfate is represented by the general formula ([Fe2(OH)n(SO4) 3-n / 2 〕m where 0 < n ≤ 2 and m is a natural number), and can be obtained by adding sodium nitrite and an oxidizing agent as a catalyst to a ferrous sulfate (FeSO4) solution, which is an iron-based raw material, and allowing an oxidation reaction to proceed (Patent Document 1). Polyaluminum chloride (commonly known as PAC) is one of the representative examples of aluminum-based inorganic flocculants. It has high treatment performance for suspended solids and dissolved organic substances, a wide optimum pH range, is hardly affected by water temperature, can reduce the flocculant addition concentration, and the treated water is not colored, so it is widely used in water purification treatment plants. PAC is a flocculant having a certain basicity (= m / 3n × 100) (Patent Document 2), and is represented by the general formula Aln(OH)mCl 3n-m (3n > m), and can be obtained by adding aluminum hydroxide to hydrochloric acid or an aluminum chloride solution and heating and pressurizing in a pressure-resistant reactor (Patent Documents 3 and 4).

[0004] Inorganic flocculants generally exhibit higher flocculation effects when their main inorganic component is concentrated, allowing for a reduction in the amount of chemical used and offering advantages in terms of transportation. For example, with ferric polysulfate, a higher concentration (over 12.5% ​​total iron concentration) compared to a standard product (over 11.0-12.5% ​​total iron concentration) with lower water content provides superior flocculation and dewatering capabilities, thereby reducing product transportation costs.

[0005] Polyaluminum chloride used as a water treatment coagulant manufactured and sold in Japan has an Al2O3 concentration of approximately 10% (by weight) or higher (hereinafter referred to as "standard products"). High-concentration products with an Al2O3 concentration exceeding 15% are not sold in Japan due to issues with solution stability, however inventions relating to high-concentration polyaluminum chloride products with an Al2O3 concentration exceeding 10% have already been reported (Patent Documents 5 and 6). Patent Document 5 discloses a method for producing a highly basic aluminum chloride solution with an Al2O3 concentration of 5-25 wt%, and Patent Document 6 discloses a high-concentration coagulant mainly composed of basic aluminum chloride with an Al2O3 concentration of 16-25%.

[0006] In recent years, attempts have been made to mix iron-based and aluminum-based flocculants to utilize their respective characteristics, and to use them as metal salt flocculants containing iron and aluminum ions (Patent Documents 7 and 8). Patent Document 7 discloses an inorganic flocculant with an Al / Fe weight ratio of 1 / 30 to 1 / 2, and Patent Document 8 discloses a flocculant using iron-containing waste hydrochloric acid with an Al / Fe molar ratio of 0.06 to 1.0. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 51-17516 [Patent Document 2] Special Publication No. 47-21401 [Patent Document 3] Special Publication No. 49-21239 [Patent Document 4] Japanese Patent Application Publication No. 09-142837 [Patent Document 5] Japanese Patent Application Publication No. 52-111496 [Patent Document 6] Japanese Patent Publication No. 2000-70609 [Patent Document 7] Japanese Patent Application Publication No. 63-7808 [Patent Document 8] Japanese Patent Application Publication No. 1-180210 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] One example of the use of metal salt coagulants containing iron and aluminum ions is that when iron-based ferric polysulfate is added to reducing wastewater, some discoloration may occur. To prevent this, it is known that coagulants containing aluminum chloride or aluminum sulfate are used. In addition, in paper mills and similar facilities, iron-based coagulants are sometimes mixed with the primarily used aluminum-based agents to provide a deodorizing effect. However, it is known that problems can arise depending on the combination. For example, while a combination of aluminum chloride and polyferric sulfate yielded a high flocculation effect, it was highly corrosive and had storage stability problems, such as the precipitation of alum due to temperature drops. A combination of aluminum sulfate and polyferric sulfate was less corrosive and had excellent stability, but it required a larger amount of chemical additive compared to other flocculants, making it economically unfeasible. Furthermore, attempts have been made to prepare metal salt flocculants containing iron and aluminum ions by mixing iron-based ferric chloride or polyferric sulfate with polyaluminum chloride, which has the highest flocculation strength among aluminum-based materials. However, these have extremely poor storage stability, such as gelling in a short period of time, and have not been commercialized. Furthermore, in metal salt flocculants containing iron ions and aluminum ions, although the main cations are iron ions in Patent Documents 7 and 8, the preparation of a metal salt flocculant (iron-containing polyaluminum chloride) having a composition in which aluminum ions are present in a large amount relative to iron ions has not been reported so far.

[0009] The first object of the present invention is to mix and combine ferric polysulfate and polyaluminum chloride, which are known to have high flocculation ability together, so as to have higher flocculation ability compared to when each is used alone, excellent storage stability, and further applicable to a wide range of treated wastewater having various characteristics, and to provide a metal salt flocculant containing iron ions and aluminum ions.

[0010] The second object of the present invention is to provide a metal salt flocculant having an Escherichia coli removing action.

Means for Solving the Problems

[0011] In order to solve these problems, the metal salt flocculant of the present invention is composed of the following technical means. [1] A metal salt flocculant, wherein in 1 liter of the metal salt flocculant, the total content of aluminum ions and iron ions is 5.7 mol or less, the molar ratio of chloride ions to iron ions (Cl / Fe) is 28 or more, the molar ratio of sulfate ions to aluminum ions in terms of aluminum oxide (SO4 / Al2O3) is 0.15 or less, and the removal rate of Escherichia coli is higher than 83%. [2] The metal salt flocculant according to [1], wherein the molar ratio of chloride ions to iron ions (Cl / Fe) is 50 or more and 104 or less. [[ID=2)] [3] The metal salt flocculant according to [1] or [2], wherein the removal rate of Escherichia coli is higher than 90%. [4] The metal salt flocculant according to [1] or [2], having a pH of 3.7 to 4.2 (100-fold diluted solution) and a specific gravity of 1.35 to 1.45. [5] A flocculant containing the metal salt flocculant according to [1] or [2]. <0000A water quality improver containing the metal salt flocculant described in [6], [1] or [2]. An odor remover containing the metal salt flocculant described in [7], [1] or [2]. A dehydrating agent containing the metal salt flocculant described in [8], [1] or [2]. A drainage colority reducer containing the metal salt flocculant described in [9], [1] or [2].

[10] A method for treating sludge drainage, comprising a step of adding the metal salt flocculant described in [1] or [2] to the sludge drainage.

[11] A method for purifying and deodorizing water, comprising a step of adding the metal salt flocculant described in [1] or [2] to water where pathogenic microorganisms are considered to be present.

[12] A new method of using the metal salt flocculant, which uses the metal salt flocculant described in [1] or [2] for removing pathogenic microorganisms in wastewater.

[13] A new method of using the metal salt flocculant, which uses the metal salt flocculant described in [1] or [2] for removing Escherichia coli in wastewater.

Advantages of the Invention

[0012] According to the first aspect of the metal salt flocculant of the present invention, by mixing and combining polyferric sulfate and polyaluminum chloride, which are known to have high flocculation ability, a metal salt flocculant containing iron ions and aluminum ions is provided, which has high flocculation ability, excellent storage stability, and can be applied to a wide range of treated drainage liquids with various characteristics.

[0013] According to the second aspect of the present invention, in addition to the above-described effects, a metal salt flocculant having an Escherichia coli removing effect is further provided.

Brief Description of the Drawings

[0014] [Figure 1] Figure 1 is a process flow diagram of a sewage treatment plant (actual machine test field 1). [Figure 2] Figure 2 is a process flow diagram of a sewage treatment plant (actual machine test field 2). [Figure 3] Figure 3 shows the sludge volume index (SVI) of the reaction tank. [Figure 4] Figure 4 shows the changes in TP concentration in the overflow water of the final sedimentation tank. [Modes for carrying out the invention]

[0015] [Metal salt flocculant 1] The inventors have discovered that by adding and mixing a predetermined amount of ferric polysulfate to polyaluminum chloride, a metal salt flocculant containing iron ions and aluminum ions with high storage stability and excellent water treatment performance can be obtained. In other words, the present invention relates to a metal salt flocculant in which the total content of aluminum ions and iron ions per liter of the metal salt flocculant is 5.7 moles or less, the molar ratio of chloride ions to iron ions (Cl / Fe) is 28 or more, and the molar ratio of sulfate ions to aluminum ions in terms of aluminum oxide (SO4 / Al2O3) is 0.15 or less. Generally, when polyaluminum chloride, which has high basicity, is mixed with ferric polysulfate, which has low basicity, the gelation reaction of the polyaluminum chloride proceeds as the pH decreases. Also, the iron ions in ferric polysulfate become insoluble by generating iron hydroxide as the pH increases. However, by adjusting the quantitative relationship of the ions constituting the metal salt flocculant of the present invention to a predetermined range, sulfate ions necessary for the stabilization of polyaluminum chloride are supplied, and gelation is suppressed. Furthermore, for the iron ions of ferric polysulfate, the supply of alkali is reduced, which allows for the maintenance of stability. Generally, the stability of a water treatment agent in solution (storage stability) is often determined by the cation concentration and the molar ratio of anions to cations. Therefore, a stable region was defined based on Al+Fe [mol / L], Cl / Fe (molar ratio), and SO4 / Al2O3 (molar ratio). Note that Cl / Al2O3 and SO4 / Fe have unique values ​​depending on the chemicals used (polyaluminum chloride and polyferric sulfate), and these molar ratios do not change even if the mixing ratio of the two chemicals is changed, so they do not need to be considered here. This allowed us to obtain a metal salt flocculant containing iron and aluminum ions, with polyaluminum chloride as the main component and ferric polysulfate added and mixed to it. This is a new finding discovered by the inventors that is not found in the prior art.

[0016] As mentioned above, attempts have been made to produce high-performance flocculants by mixing ferric chloride or polyferric sulfate with polyaluminum chloride, but these have not been successful due to the poor storage stability of the mixture. This long-standing problem has been solved in the present invention by adjusting the anion / cation (molar ratio), and the inventors of this invention speculate that the following mechanism may be responsible.

[0017] In other words, polyaluminum chloride, used as a flocculant, often contains sulfate ions, and these sulfate ions are thought to contribute to the flocculation properties and chemical stability of polyaluminum chloride. In this invention, by adjusting the sulfate ion content and adding sulfate ions in the form of polyferric sulfate, not only is the chemical stability of the mixture improved, but although it has not been confirmed, it is possible that the proportion of a certain polynuclear complex (multimer) formed by aluminum ions and iron ions is increased, and it is presumed that this contributes to the improvement of the water treatment properties of the metal salt coagulant of this invention. In fact, as will be specifically described below, the metal salt flocculant of the present invention is a flocculant that exhibits remarkable effects over a wide range of applications.

[0018] The polyaluminum chloride used in this invention preferably has an Al concentration in the range of 2 to 6 mol / L. Similarly, the ferric polysulfate preferably has an Fe concentration in the range of 2 to 4 mol / L. If the amount of ferric polysulfate added is too small, the stability of the iron-containing polyaluminum chloride is poor, and it cannot exhibit good flocculation ability. On the other hand, if the amount added is too large, hydrolysis of the ferric polysulfate progresses, and iron-based deposits precipitate as byproducts, which is undesirable. The metal salt flocculant obtained in the present invention preferably has a pH of 3.7 to 4.2 (100-fold diluted solution) and a specific gravity of 1.35 to 1.45.

[0019] The resulting metal salt coagulant is not only excellent as a coagulant, but also excels in the removal of phosphorus, nitrogen, COD, or SS, and also possesses superior performance in deodorization, dewatering, color reduction, bacterial and viral removal, and fluorine and TOC removal. Therefore, taking advantage of these properties, it can be used not only as a coagulant but also as a versatile wastewater treatment agent for a wide range of applications.

[0020] (others) As is evident from the actual tests in the chromaticity reduction test described later, the metal salt flocculant according to the first embodiment can be injected using the same equipment as conventional polyaluminum chloride. Furthermore, because the amount of chemical used can be reduced, the frequency of tanker truck transport and receiving decreases. This leads to a reduction in necessary labor and personnel costs.

[0021] [Metal salt flocculant 2] While the present invention has been described primarily in relation to the metal salt flocculant according to the first embodiment, the present invention is not limited to the above. The differences from the metal salt flocculant according to the first embodiment will be described in detail.

[0022] In water treatment plants, in addition to the processes mentioned above, such as sludge sedimentation and phosphorus / nitrogen removal, E. coli removal was also carried out. Traditionally, these processes—sludge sedimentation and E. coli removal—were carried out in separate stages using different chemicals. In recent years, awareness of reducing environmental impact has been increasing, as exemplified by the term Sustainable Development Goals (SDGs). In the field of water treatment, there has been a demand to reduce the amount of chemicals used in water treatment, thereby reducing the power consumption of equipment such as pumps that add chemicals, and to reduce the release of carbon dioxide when chemicals are transported by tank trucks. The inventors of this invention have sincerely investigated ways to further improve the functionality of metal salt flocculants and have found that, in addition to the basic performance described above, metal salt flocculants also possess the function of removing E. coli.

[0023] That is, the metal salt flocculant according to the second embodiment is a metal salt flocculant in which the total content of aluminum ions and iron ions per liter of the metal salt flocculant is 5.7 moles or less, the molar ratio of chloride ions to iron ions (Cl / Fe) is 28 or more, the molar ratio of sulfate ions to aluminum ions in terms of aluminum oxide (SO4 / Al2O3) is 0.15 or less, and the removal rate of E. coli is higher than 83%.

[0024] According to the metal salt coagulant of the second embodiment, sludge sedimentation and E. coli removal can be performed in a single step using one type of agent, thereby simplifying the overall water treatment process. Furthermore, by making the agents used in water treatment more multifunctional, the total amount of agents used in water treatment can be reduced, and as a result, energy consumption during agent transportation can also be reduced.

[0025] The mechanism by which the metal salt flocculant according to the second embodiment removes E. coli is not entirely clear, but it is thought that the E. coli are captured in flocs along with the sludge due to the flocculation and sedimentation effect, and then discharged as excess sludge in the final sedimentation tank. It is also thought that the residual chlorine derived from the chemical agent has a bactericidal effect.

[0026] To improve the effectiveness of removing E. coli, it is preferable to have a high concentration of chloride ions. Specifically, the molar ratio of chloride ions to iron ions (Cl / Fe) is preferably 28 or higher, and more preferably 50 to 104. Below 28, the chemical stability of the disinfectant is low, leading to the precipitation of iron hydroxide. Above 104, the side effects due to the coexistence of iron ions are reduced, and there is a risk of excessive residual chlorine in the treated water. While a high level of residual chlorine in the treated water increases the duration of the disinfection effect, there are concerns about adverse effects on aquatic organisms inhabiting the water bodies to which the water is discharged. Furthermore, the removal rate of E. coli is more preferably higher than 90%.

[0027] The present invention is not limited to metal salt flocculants, but also relates to various methods that utilize the properties of the metal salt flocculants 1 and 2 described above.

[0028] [Methods for treating sludge wastewater] This invention relates to sludge treatment and wastewater treatment in sewage treatment. In other words, the present invention relates to a method for treating sludge wastewater, comprising the step of adding the above-mentioned metal salt coagulant 1 or 2 to the sludge wastewater. As described later in the Examples section, metal salt coagulants 1 or 2 exhibit excellent effects in terms of phosphorus and nitrogen removal performance, deodorizing properties (hydrogen sulfide suppression effect), color reduction, and sludge settling properties (SV value). Furthermore, compared to the case where polyaluminum chloride is used as the agent, sludge settling properties are improved with an addition rate of approximately 50% of the amount of polyaluminum chloride added, and phosphorus removal performance equivalent to that of polyaluminum chloride is achieved.

[0029] When metal salt coagulant 2 is added, in addition to the above-mentioned performance, it also exhibits a removal effect on pathogenic microorganisms, such as E. coli. By adding metal salt coagulant 2 to the sludge, the removal rate of E. coli becomes higher than 83%, preferably higher than 90%. Considering that the removal rate of E. coli when polyaluminum chloride is added as a chemical agent is about 75%, metal salt flocculant 2 can significantly improve the removal rate of E. coli even when added at an amount less than 50% of the amount of polyaluminum chloride added. This method allows for sludge sedimentation and E. coli removal to be performed in a single step using one type of chemical, thereby simultaneously simplifying the work process and reducing the amount of chemicals used in the overall water treatment.

[0030] [Methods for purifying and deodorizing water] In addition to sewage treatment, the present invention also relates to a method for purifying and deodorizing wastewater such as drinking water and reclaimed water. In other words, the present invention also relates to a water purification and deodorization method comprising the step of adding the above-mentioned metal salt coagulant 1 or 2 to water in which pathogenic microorganisms are thought to be present. Despite the small amount of chemicals added, water purification and deodorization can be achieved through phosphorus and nitrogen removal performance, deodorizing properties (hydrogen sulfide suppression effect), color reduction, and pathogenic microorganism removal properties.

[0031] [Other Embodiments] As described above, the present invention has been described by embodiments, but the descriptions and drawings that constitute part of this disclosure should not be understood as limiting the invention. Various alternative embodiments, examples, and operational techniques will become apparent to those skilled in the art from this disclosure. For example, the metal salt flocculant described in the embodiment can be used in new ways of use. That is, the present invention relates to new ways of using the metal salt flocculant 1 or 2 described above for the removal of pathogenic microorganisms in wastewater, and to new ways of using the metal salt flocculant 1 or 2 described above for the removal of Escherichia coli in wastewater. Thus, the present invention naturally includes various embodiments and the like that are not described herein. Therefore, the technical scope of the present invention is determined solely by the inventive features relating to the claims that are appropriate from the above description. [Examples]

[0032] [Metal salt flocculant 1] The following experiments were conducted with respect to the metal salt flocculant according to the first embodiment. (Characteristic evaluation) The properties of the prepared metal salt flocculants were evaluated from the following perspectives. (1) Sludge settling properties (SV value) Activated sludge was filled into a 1-liter graduated cylinder, and each of the chemicals to be evaluated was added to it. After standing for a predetermined time, the sludge settling properties of each chemical were evaluated from the sludge height obtained by solid-liquid separation. Here, in SVn, SV represents the sludge volume and n represents the elapsed time (minutes) after standing. (2) Removal characteristics of TP, TN, COD, and SS components The supernatant water was tested after adding each of the target chemicals to activated sludge and allowing it to stand for one hour. TP represents total phosphorus, TN represents total nitrogen, COD represents chemical oxygen demand, and SS represents suspended solids. The removal characteristics of each chemical were evaluated based on the remaining amounts [mg / L] of these components. (3) Deodorizing properties (hydrogen sulfide suppression effect) Each of the chemicals to be evaluated was added to raw sludge and allowed to stand for 4 hours. The hydrogen sulfide concentration (H2S [ppm]) in the supernatant water was measured using a gas detector. A lower concentration of residual hydrogen sulfide in the supernatant water indicates superior deodorizing properties. (4) Dehydration Each of the chemicals to be evaluated was added to the digested sludge, and the moisture content [%] of the cake after pressurization and dewatering was measured. (5) Decrease in chromaticity Each of the chemicals under evaluation was added to the biological reaction tank of a sewage treatment plant, and the color of the overflow water in the final sedimentation tank was measured. [Example 1]

[0033] (Drug preparation and stability evaluation) Polyaluminum chloride with varying Al concentrations of 5.08 to 5.87 mol / L was mixed and added to ferric polysulfate with an Fe concentration of 2.93 mol / L and a specific gravity of 1.484 in 250 mL poly bottles, with the SO4 / Al2O3 molar ratio of each component ranging from 0.07 to 0.17. 200 g of the mixture was obtained. 1 g of the resulting sample was taken, diluted with 100 mL of pure water, and the pH of the solution was measured. The remaining sample was measured for specific gravity, stored at room temperature for one month, and its storage stability was evaluated. The mixing conditions for polyaluminum chloride and polyferric sulfate are shown in terms of the molar amounts of each component (Al and Fe), and the stability of the metal salt flocculant of the present invention after mixing is shown in Table 1.

[0034] [Table 1]

[0035] From the experimental results summarized in Table 1, it can be seen that the metal salt flocculant of the present invention is stably present when the total of aluminum ions and iron ions is 5.7 mol or less per liter, the molar ratio of chloride ions to iron ions (Cl / Fe) is 28 or more, and the molar ratio of sulfate ions to aluminum ions in terms of aluminum oxide (SO4 / Al2O3) is 0.15 or less. [Example 2]

[0036] (Sludge sedimentation property and removal characteristics of each component) 1,000 mL of activated sludge (TS: 0.2%) sampled from a sewage treatment plant was collected in a 1 L graduated cylinder, and polyaluminum chloride (M 3+ 2.5 mol / L), ferric polysulfate (M 3+ 2.9 mol / L), and the metal salt flocculant of the present invention (M 3+ 5.3 mol / L (Al 3+ 5.1 mol / L, Fe 3+ 0.2 mol / L), Cl / Fe: 65, SO4 / Al2O3: 0.04) were added and mixed under the conditions shown in Table 2. After standing for 10 minutes and then for 30 minutes, the sludge sedimentation properties (SV 10 [[ID=2 / span>0]]、SV 30 ) were measured. Here, M 3+ represents the total concentration of trivalent metal ions (i.e., Al 3+ and Fe 3+ ) contained in the chemical agent. Furthermore, for the supernatant water after standing for 1 hour, the amounts of each component of residual T-P, T-N, COD, and SS were analyzed. The addition amounts of each chemical agent were set so that M 3+ were all equal, as shown in Table 2. The test results are as shown in Table 2. Here, TS is an abbreviation for total evaporation residue, and here it indicates the amount of sludge as solids.

[0037]

Table 2

[0038] (Evaluation of sludge sedimentation property) When each agent was added to activated sludge, the metal salt flocculant of the present invention showed the best sludge settling properties (SV value) with a smaller addition amount than polyaluminum chloride and polyferric sulfate. 10 Focusing on the values, a significant difference was observed in the initial sedimentation velocity, indicating that the drug has excellent immediate effects. The use of the metal salt coagulant of the present invention greatly improves the solid-liquid separation properties of treated water, making it usable in all water treatment facilities for the purpose of coagulation (e.g., coagulation tanks, biological reaction tanks, gravity thickening tanks, etc.).

[0039] (Evaluation of removal characteristics of TP, TN, COD, and SS components) The metal salt flocculant of the present invention was able to remove more TP, TN, COD, and SS from the supernatant water with a smaller amount of additive compared to polyaluminum chloride or polyferric sulfate. Therefore, since the use of the metal salt coagulant of the present invention enables the efficient removal and recovery of the above components, it is expected to be effective in combating eutrophication and improving water quality. [Example 3]

[0040] (Deodorizing and hydrogen sulfide suppression) Raw sludge (TS 1.1%) sampled from a sewage treatment plant was collected in a 1L graduated cylinder in a 1,000mL volume. The polyaluminum chloride, polyferric sulfate, and the metal salt coagulant of the present invention used in Example 2 were added and mixed under the conditions shown in Table 3. After standing for 4 hours, 100mL of the supernatant water was collected in a 300mL Erlenmeyer flask, sealed tightly, and shaken. The hydrogen sulfide concentration in the gas phase was then measured using a gas detection tube. The amount of each agent added was set to equalize the concentration of trivalent metal ions, as described above. The test results are shown in Table 3.

[0041] [Table 3]

[0042] (Evaluation of deodorizing properties) The hydrogen sulfide removal rates were in the order of polyaluminum chloride < metal salt flocculant of the present invention < polyferric sulfate. Generally, the immobilization of sulfur by iron ions contributes significantly to the suppression of hydrogen sulfide, so the metal salt flocculant of the present invention showed a higher hydrogen sulfide suppression effect compared to ordinary polyaluminum chloride. Therefore, the metal salt coagulant of the present invention can also be used for deodorizing purposes in water treatment. Examples of use include sewage treatment plants, wastewater treatment facilities, pumping stations, and sludge transport facilities. [Example 4]

[0043] (Dehydration properties) Digested sludge (TS 1.3%) sampled from a sewage treatment plant was collected in a 500 mL beaker in a 300 mL container. The inorganic flocculants used in Example 2 (polyaluminum chloride, polyferric sulfate, and the metal salt flocculant of the present invention) and polymer flocculants (0.3 wt%, 170 ppm) were added and mixed under the conditions shown in Table 4. After filtering for 60 seconds, the mixture was pressurized and dewatered, and the cake moisture content was measured. The amount of chemicals added was set to equalize the concentration of trivalent metal ions, as described above. The test results are shown in Table 4.

[0044] [Table 4]

[0045] (Evaluation of dehydration properties) Dewatering properties were best in the order of polyaluminum chloride < polyferric sulfate < the metal salt flocculant of the present invention. With the metal salt flocculant of the present invention, the moisture content of the cake decreased by 1.5 percentage points compared to when no agent was added. Based on the above, the metal salt coagulant of the present invention can also be used in dewatering machines to reduce the water content of sludge, ultimately leading to a reduction in sludge transportation and treatment costs. [Example 5]

[0046] (chromaticity reduction characteristic) The flow of wastewater treatment plants shown in Figure 1 (average daily inflow: approximately 33,000 m³) 3For one week, polyaluminum chloride (25 mg / L) used in Example 2 or the metal salt coagulant of the present invention (14 mg / L) was continuously injected into the terminal end of the biological reaction tank of the standard activated sludge method. The agent was added into the liquid in the biological reaction tank using a diaphragm-type metering pump. The amount of agent added was set to equalize the concentration of trivalent metal ions, as described above. Overflow water was periodically sampled from the final sedimentation tank downstream of the biological reaction tank, and its color was measured. The test results are shown in Table 5. Here, the average and minimum values ​​of chromaticity are the weekly averages.

[0047] [Table 5]

[0048] (Evaluation of chromaticity reduction characteristics) With the metal salt flocculant of the present invention, a significant decrease in color was observed even with a smaller amount added than with polyaluminum chloride. Therefore, the chemical agent of the present invention is expected to be used not only in sewage but also in wastewater such as drinking water and reclaimed water.

[0049] (Other advantages) Actual field tests in color degradation tests showed that the metal salt flocculant of the present invention could be injected using the same equipment as conventional polyaluminum chloride. Furthermore, because the amount of chemical used can be reduced, the frequency of tanker truck transport and receiving decreases, which leads to a reduction in necessary labor and personnel costs.

[0050] [Metal salt flocculant 2] [Example 6], [Comparative Example 1] The following experiments were conducted on the metal salt flocculant according to the second embodiment. (Actual machine testing) (Facility Overview) Actual-scale tests were conducted using a treatment plant equipped with treatment facilities (System A) and (System B) as shown in the flow diagram in Figure 2. The average daily inflow volume of the treatment plant was 34,000 m³. 3The treatment is carried out daily using a standard activated sludge process, and six lines operate using a pseudo-step-inflow two-stage nitrification-denitrification method for nitrogen removal. In addition, to perform advanced phosphorus treatment, polyaluminum chloride (PAC) is added as a coagulant before the final tank in one of the reaction tanks (coagulant-assisted step-inflow two-stage nitrification-denitrification method). A portion of the treated water undergoes sand filtration, ozone treatment, and chlorine disinfection before being reused as water for recreational use in a nearby park.

[0051] (Test method) As the flocculant to be injected, in Comparative Example 1, commercially available polyaluminum chloride (PAC) (specific gravity: 1.214, Cl / Al2O3: 2.7) was used, and in Example 6, high-concentration iron-aluminum (specific gravity: 1.445, Cl / Fe: 63, SO4 / Al2O3: 0.08, Cl / Al2O3: 3.3, SO4 / Fe: 1.4) was used. The concentration of trivalent metal ions contained in the agent (Al 3+ Fe 3+ The concentrations were 2.38 mol / L for Comparative Example 1 (PAC) and 5.35 mol / L for Example 6 (high-concentration ferroaluminum). PAC and high-concentration ferroaluminum were added to a treatment facility (System A) using a step-inflow, two-stage nitrification-denitrification method with a coagulant. The chemicals were injected before the final tank of the reaction tank, and PAC and high-concentration ferroaluminum were injected using a metering pump for two weeks each (addition rate: Comparative Example 1 (PAC): 34 mg / L, Example 6 (high-concentration ferroaluminum): 17 mg / L). In addition, a treatment facility (System B) using the standard activated sludge method (pseudo-step-inflow, two-stage nitrification-denitrification method) was selected as a blank. Activated sludge from the final tank of the reaction tanks in Systems A and B, and overflow water from the final sedimentation tank were sampled periodically to evaluate sludge settling properties and water quality. The tests were conducted from November 26, 2020 to December 17, 2020.

[0052] (Test results) (Evaluation of sludge settling properties) Figure 3 shows the sludge volume index (SVI) of the reaction tank. Compared to the blank B system's SVI of 300-400 mL / g, the A system's SVI was 150-300 mL / g during PAC injection and 100-200 mL / g during high-concentration iron-aluminum injection. The injection of coagulants improved the sludge's settling properties, and high-concentration iron-aluminum, in particular, was thought to have a higher coagulation effect.

[0053] (Evaluation of phosphorus and nitrogen removal performance) Figure 4 shows the changes in TP concentration in the overflow water of the final sedimentation tank. The TP concentration in system A remained constant between 0.05 and 0.50 mg / L during the injection period of PAC and high-concentration iron-aluminum. Although the addition rate of high-concentration iron-aluminum was approximately 50% of that of PAC, it was shown that equivalent phosphorus removal could be achieved because the metal ion concentration was the same as that of PAC. Furthermore, there was no significant difference in TN concentration when PAC and high-concentration iron-aluminum were injected, suggesting that the nitrogen removal performance by biological reaction remained constant.

[0054] (Evaluation of E. coli and odor substance removal) Table 6 shows the analysis results for the number of E. coli bacteria, residual chlorine concentration, and odor substance concentrations (geosmin, 2-methylisoborneol) of the overflow water from the final sedimentation tank. [Table 6] The number of E. coli in system A was lower than in system B (which was a blank), and the removal rate was approximately 75-83% during PAC injection and about 90% during high-concentration iron-aluminum injection. The residual chlorine (free residual chlorine and combined residual chlorine) concentrations were similar in both systems A and B, and the values ​​were low, suggesting that they were not at a concentration that would provide disinfection. It is generally believed that some pathogenic microorganisms in sewage (such as E. coli, norovirus, and Cryptosporidium) are adsorbed onto sludge, become trapped in flocs, and are removed from the treated water through coagulation and sedimentation. The number of E. coli correlated with the SVI values ​​of both the A and B systems, and since there were no chlorine components with disinfectant properties in the treated water, it is thought that E. coli was removed from the treated water through coagulation and sedimentation in this test. Furthermore, E. coli was not detected in the reclaimed water after sand filtration, ozone treatment, and chlorine disinfection. The odor substance concentrations were low in both system A and system B, and there was no significant difference in the analytical values. Therefore, no superior deodorizing effect was confirmed by injecting the coagulant in this test.

[0055] (chromaticity, turbidity) Table 7 shows the measurement results for the color and turbidity of the water overflowing from the final sedimentation tank. [Table 7] The chromaticity of system A was lower than that of system B, indicating that the clarity of the treated water improved with the injection of the coagulant. The chromaticity when high-concentration iron-aluminum was injected was 10 degrees, which is below the standard level for water-friendly water (10 degrees or less). The turbidity was around 2.0 regardless of the type of coagulant, and no significant difference was observed in the analytical values ​​of systems A and B.

[0056] (Possibility of using treated water with coagulants as recycled wastewater) The uses of recycled wastewater include (1) flushing water, (2) watering water, (3) landscaping water, and (4) waterfront water use. Water quality standards include coliform count, turbidity, pH, appearance, color, and odor. Based on these items, the degree of water quality improvement through the use of coagulants was evaluated. In this test, the blank treated water was excluded from evaluation because its turbidity and odor concentration were low. As mentioned above, the injection of coagulants is effective in reducing color, and this test showed that it improved to the standard level. Regarding the number of E. coli, the injection of coagulants was able to remove 75-90% of E. coli from the treated water. However, it did not meet the criteria of (1), (2), and (4), which is "not detectable," or the standard value of 10 CFU / mL for (3). Therefore, it is currently difficult to achieve the standard value for the number of E. coli with coagulant injection alone, and it is considered necessary to combine it with more advanced treatment (chlorine disinfection and ozone treatment) in order to use the treated water as recycled water. When using coagulants, the removal rate of E. coli largely depends on the coagulation capacity of the coagulant used. Therefore, increasing the number of cations injected can be expected to yield a higher removal rate, but the appropriate injection rate needs to be considered in conjunction with other factors such as pH. In this coagulant injection test, the water quality of the treated water did not improve to the standard level for recycled wastewater in terms of E. coli count, but it was found that the use of coagulants can reduce the concentration of pathogenic microorganisms by a certain percentage. Reducing the concentration of pathogenic microorganisms in treated water in wastewater treatment is equivalent to reducing the risk of pathogen exposure for workers. Therefore, the use of coagulants is considered significant not only for improving wastewater treatment capacity but also for reducing the risk of infection for workers at treatment plants.

[0057] In a chemical injection test into a biological treatment system aimed at nitrogen and phosphorus removal, high-concentration iron-aluminum improved sludge settling properties at approximately 50% of the addition rate of PAC, demonstrating phosphorus removal performance equivalent to that of PAC. The injection of a coagulant reduced the number of E. coli bacteria by approximately 75-90%. It is believed that E. coli is removed through the coagulation and sedimentation of sludge, and the use of a coagulant was expected to improve the removal rate of pathogenic microorganisms adsorbed on the sludge. While the removal of E. coli from sewage by injecting coagulants did not reach the standard values ​​for recycled sewage, it was shown that this could be improved by adjusting the amount added. A reduction in the concentration of pathogenic microorganisms in treated water leads to a reduction in the risk of pathogen exposure for workers at treatment plants, and the use of coagulants is thought to contribute to such risk reduction.

Claims

1. A metal salt flocculant, The total content of aluminum ions and iron ions in 1 liter of metal salt flocculant is 5.7 moles or less. The raw materials used are ferric polysulfate and polyaluminum chloride, and the molar ratio of chloride ions to iron ions (Cl / Fe) is 28 or higher. The molar ratio of aluminum ions in terms of sulfate ions to aluminum oxide (SO ４ / Al ２ O ３ ) is 0.15 or less, A metal salt flocculant with an E. coli removal rate higher than 83%.

2. The metal salt flocculant according to claim 1, wherein the molar ratio of chloride ions to iron ions (Cl / Fe) is 50 or more and 104 or less.

3. A metal salt flocculant according to claim 1 or 2, wherein the removal rate of E. coli is higher than 90%.

4. A flocculant containing the metal salt flocculant described in claim 1 or 2.

5. A water quality improver containing the metal salt coagulant described in claim 1 or 2.

6. A deodorant containing the metal salt flocculant described in claim 1 or 2.

7. A dehydrating agent containing the metal salt flocculant described in claim 1 or 2.

8. A wastewater color reducer containing the metal salt coagulant described in claim 1 or 2.

9. A method for treating sludge wastewater, comprising the step of adding a metal salt coagulant according to claim 1 or 2 to the sludge wastewater.

10. A method for purifying and deodorizing water, comprising the step of adding a metal salt coagulant according to claim 1 or 2 to water in which pathogenic microorganisms are thought to be present.

11. A novel method for using a metal salt coagulant according to claim 1 or 2 for the removal of pathogenic microorganisms in wastewater.

12. A new method for using a metal salt coagulant according to claim 1 or 2 to remove E. coli from wastewater.

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